Cultured mammalian cells and small nematodes are being used as model systems to study the mechanisms of aging. During the coming year, several related projects with WI-38 cells will be continued. Nutritional requirements will be determined in detail, and improved media with all nutrients at experimentally determined optimum concentrations will be prepared and tested for effects on cellular aging. High voltage electron microscopy will be used to compare three-dimensional cytoplasmic organization of "young" and "old" cells. Techniques for reconstruction of visable cells from isolated karyoplasts and cytoplasts will be developed further, and attempts will be made to study reconstructed cells containing young nuclei and old cytoplasms and vice versa. DNA synthesis induced by fusion to S-phase cells will also be used to search for differences in patterns of DNA synthesis of young and old cells. Aging in Caenorhabditis elegans will be studied at the ultrastrutural and cytochemical levels. Mutants with altered lifespans will be isolated and the mechanisms responsible will be analyzed. The long-term goal of the research program is to understand aging in terms of molecular events occurring within and among the individual cells of aging organisms.